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List allowed tokens after macro fragments #55301

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merged 1 commit into from
Oct 26, 2018
Merged

List allowed tokens after macro fragments #55301

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138 changes: 94 additions & 44 deletions src/libsyntax/ext/tt/macro_rules.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -792,15 +792,15 @@ fn check_matcher_core(sess: &ParseSess,
if let TokenTree::MetaVarDecl(_, ref name, ref frag_spec) = *token {
for next_token in &suffix_first.tokens {
match is_in_follow(next_token, &frag_spec.as_str()) {
Err((msg, help)) => {
IsInFollow::Invalid(msg, help) => {
sess.span_diagnostic.struct_span_err(next_token.span(), &msg)
.help(help).emit();
// don't bother reporting every source of
// conflict for a particular element of `last`.
continue 'each_last;
}
Ok(true) => {}
Ok(false) => {
IsInFollow::Yes => {}
IsInFollow::No(ref possible) => {
let may_be = if last.tokens.len() == 1 &&
suffix_first.tokens.len() == 1
{
Expand All @@ -809,15 +809,41 @@ fn check_matcher_core(sess: &ParseSess,
"may be"
};

sess.span_diagnostic.span_err(
next_token.span(),
let sp = next_token.span();
let mut err = sess.span_diagnostic.struct_span_err(
sp,
&format!("`${name}:{frag}` {may_be} followed by `{next}`, which \
is not allowed for `{frag}` fragments",
name=name,
frag=frag_spec,
next=quoted_tt_to_string(next_token),
may_be=may_be)
may_be=may_be),
);
err.span_label(
sp,
format!("not allowed after `{}` fragments", frag_spec),
);
let msg = "allowed there are: ";
match &possible[..] {
&[] => {}
&[t] => {
err.note(&format!(
"only {} is allowed after `{}` fragments",
t,
frag_spec,
));
}
ts => {
err.note(&format!(
"{}{} or {}",
msg,
ts[..ts.len() - 1].iter().map(|s| *s)
.collect::<Vec<_>>().join(", "),
ts[ts.len() - 1],
));
}
}
err.emit();
}
}
}
Expand Down Expand Up @@ -860,6 +886,12 @@ fn frag_can_be_followed_by_any(frag: &str) -> bool {
}
}

enum IsInFollow {
Yes,
No(Vec<&'static str>),
Invalid(String, &'static str),
}

/// True if `frag` can legally be followed by the token `tok`. For
/// fragments that can consume an unbounded number of tokens, `tok`
/// must be within a well-defined follow set. This is intended to
Expand All @@ -868,81 +900,99 @@ fn frag_can_be_followed_by_any(frag: &str) -> bool {
/// break macros that were relying on that binary operator as a
/// separator.
// when changing this do not forget to update doc/book/macros.md!
fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> Result<bool, (String, &'static str)> {
fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> IsInFollow {
use self::quoted::TokenTree;

if let TokenTree::Token(_, token::CloseDelim(_)) = *tok {
// closing a token tree can never be matched by any fragment;
// iow, we always require that `(` and `)` match, etc.
Ok(true)
IsInFollow::Yes
} else {
match frag {
"item" => {
// since items *must* be followed by either a `;` or a `}`, we can
// accept anything after them
Ok(true)
IsInFollow::Yes
},
"block" => {
// anything can follow block, the braces provide an easy boundary to
// maintain
Ok(true)
IsInFollow::Yes
},
"stmt" | "expr" => match *tok {
TokenTree::Token(_, ref tok) => match *tok {
FatArrow | Comma | Semi => Ok(true),
_ => Ok(false)
},
_ => Ok(false),
"stmt" | "expr" => {
let tokens = vec!["`=>`", "`,`", "`;`"];
match *tok {
TokenTree::Token(_, ref tok) => match *tok {
FatArrow | Comma | Semi => IsInFollow::Yes,
_ => IsInFollow::No(tokens),
},
_ => IsInFollow::No(tokens),
}
},
"pat" => match *tok {
TokenTree::Token(_, ref tok) => match *tok {
FatArrow | Comma | Eq | BinOp(token::Or) => Ok(true),
Ident(i, false) if i.name == "if" || i.name == "in" => Ok(true),
_ => Ok(false)
},
_ => Ok(false),
"pat" => {
let tokens = vec!["`=>`", "`,`", "`=`", "`|`", "`if`", "`in`"];
match *tok {
TokenTree::Token(_, ref tok) => match *tok {
FatArrow | Comma | Eq | BinOp(token::Or) => IsInFollow::Yes,
Ident(i, false) if i.name == "if" || i.name == "in" => IsInFollow::Yes,
_ => IsInFollow::No(tokens),
},
_ => IsInFollow::No(tokens),
}
},
"path" | "ty" => match *tok {
TokenTree::Token(_, ref tok) => match *tok {
OpenDelim(token::DelimToken::Brace) | OpenDelim(token::DelimToken::Bracket) |
Comma | FatArrow | Colon | Eq | Gt | BinOp(token::Shr) | Semi |
BinOp(token::Or) => Ok(true),
Ident(i, false) if i.name == "as" || i.name == "where" => Ok(true),
_ => Ok(false)
},
TokenTree::MetaVarDecl(_, _, frag) if frag.name == "block" => Ok(true),
_ => Ok(false),
"path" | "ty" => {
let tokens = vec![
"`{`", "`[`", "`=>`", "`,`", "`>`","`=`", "`:`", "`;`", "`|`", "`as`",
"`where`",
];
match *tok {
TokenTree::Token(_, ref tok) => match *tok {
OpenDelim(token::DelimToken::Brace) |
OpenDelim(token::DelimToken::Bracket) |
Comma | FatArrow | Colon | Eq | Gt | BinOp(token::Shr) | Semi |
BinOp(token::Or) => IsInFollow::Yes,
Ident(i, false) if i.name == "as" || i.name == "where" => IsInFollow::Yes,
_ => IsInFollow::No(tokens),
},
TokenTree::MetaVarDecl(_, _, frag) if frag.name == "block" => IsInFollow::Yes,
_ => IsInFollow::No(tokens),
}
},
"ident" | "lifetime" => {
// being a single token, idents and lifetimes are harmless
Ok(true)
IsInFollow::Yes
},
"literal" => {
// literals may be of a single token, or two tokens (negative numbers)
Ok(true)
IsInFollow::Yes
},
"meta" | "tt" => {
// being either a single token or a delimited sequence, tt is
// harmless
Ok(true)
IsInFollow::Yes
},
"vis" => {
// Explicitly disallow `priv`, on the off chance it comes back.
let tokens = vec!["`,`", "an ident", "a type"];
match *tok {
TokenTree::Token(_, ref tok) => match *tok {
Comma => Ok(true),
Ident(i, is_raw) if is_raw || i.name != "priv" => Ok(true),
ref tok => Ok(tok.can_begin_type())
Comma => IsInFollow::Yes,
Ident(i, is_raw) if is_raw || i.name != "priv" => IsInFollow::Yes,
ref tok => if tok.can_begin_type() {
IsInFollow::Yes
} else {
IsInFollow::No(tokens)
}
},
TokenTree::MetaVarDecl(_, _, frag) if frag.name == "ident"
|| frag.name == "ty"
|| frag.name == "path" => Ok(true),
_ => Ok(false)
|| frag.name == "path" => IsInFollow::Yes,
_ => IsInFollow::No(tokens),
}
},
"" => Ok(true), // keywords::Invalid
_ => Err((format!("invalid fragment specifier `{}`", frag),
VALID_FRAGMENT_NAMES_MSG))
"" => IsInFollow::Yes, // keywords::Invalid
_ => IsInFollow::Invalid(format!("invalid fragment specifier `{}`", frag),
VALID_FRAGMENT_NAMES_MSG),
}
}
}
Expand Down
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